Various electronic apparatuses are developed for improving human life. Nevertheless, there are still many technical issues to make these electronic apparatuses more convenient to increase their applications. Today, most network environment is composed of multiple homogeneous or heterogeneous sub networks. For example, the Internet serves as a main body, and multiple gateways and routers are used to connect private local networks used at home, or private networks behind telecommunication service providers. Under such configuration, if a user wants to connect two terminal devices via a point-to-point connection, it is still very complicated particularly when the two terminal devices are located at different sub-networks. Specifically, if the two terminal devices are located behind different NAT (Network Address Translation) devices, they may have separate private network addresses. In addition, it is always challenging to efficiently and easily establish a network connection.